Device for determining the level of contents in a container

ABSTRACT

The invention relates to a level sensor ( 1 ). The aim of the invention is to provide a level sensor ( 1 ) which is capable of largely eliminating the influence of the structural parts ( 4 ) and/or of the formation of deposits on the measuring accuracy and on the measuring sensitivity of the level sensor ( 1 ). To this end, the invention provides, among other things, that the launching unit ( 2 ) has at least one length, which essentially corresponds to the distance from the container wall ( 3 ) to the lower edge ( 5 ) of the structural part ( 4 ) and which is positioned in such a manner that the transition area launching unit conductive element is located approximately in the plane of the lower edge ( 5 ) of the structural part ( 4 ), and that the diameter of the opening ( 8 ) of the launching unit ( 2 ) on the transition launching unit conductive element ( 6 ) is in the order of magnitude of the wavelength of the high-frequency measurement signals.

[0001] The invention relates to a device for determining the level ofcontents in a container, as generically defined by the preamble to theindependent claims. It is understood that the device is also suitablefor determining the location of at least one boundary face between twophases of a medium or between two media.

[0002] For determining the level of contents in a container, measuringsystems are used that measure different physical variables. On the basisof these variables, the desired information about the level is thenderived. Besides mechanical scanners, capacitive, conductive orhydrostatic measuring probes are used, as are detectors that operate onthe basis of ultrasound, microwaves, or radioactive radiation.

[0003] In many fields of use, such as petrochemicals, chemistry and thefood industry, highly accurate measurements of the level of liquids orbulk goods in containers (tanks, silos, etc.) are needed. Increasingly,sensors are therefore used in which brief electromagnetic high-frequencypulses (TDR methods or pulse-radar methods) or continuousfrequency-modulated microwaves (such as FMCW-radar methods) are inputinto a conductive element or a waveguide and carried into the containerwhere the contents are stored by means of the waveguide. The knownvariants can be considered as the waveguide: surface waveguides on theSommerfeld or Goubau principle, or Lecher waveguides.

[0004] In physical terms, in this measuring method, the effect isexploited that at the boundary face between two different media, such asair and oil or air and water, some of the guided high-frequency pulsesor the guided microwaves carried are reflected because of the abruptchange (discontinuity) in the dielectric constants of both media and isreturned back to a receiver by way of the conductive element. Thereflected component (or useful echo signal) is all the greater, thegreater the difference between the dielectric constants of the twomedia. The distance from the surface of the contents can be determinedfrom the transit time of the reflected component of the high-frequencypulses or CW signals (echo signals). If the empty distance of thecontainer is known, then the level of contents in the container can becalculated. If a boundary face determination is to be performed, thenthe location of the boundary face can be determined from the outcomes ofthe measurement.

[0005] Sensors with guided high-frequency signals (pulses or waves) aredistinguished over sensors that freely broadcast high-frequency pulsesor waves (free-field microwave systems or FMR, also called “genuineradar systems”) in having a substantially greater echo amplitude. Thereason for this is that the power flow is effected quite purposefullyalong the waveguide or conductive element. Moreover, sensors with guidedhigh-frequency signals have greater measuring sensitivity and measuringaccuracy at close range than freely broadcasting sensors.

[0006] The measuring accuracy and measuring sensitivity of sensors thatuse surface or Lecher waveguides is worsened considerably if thetransition region from the input unit to the conductive element islocated in the region of a container connection stub or—in generalterms—in the region of a structural part that is disposed in thecontainer. If that is the case, then there is the risk that the portionof the radiation that is not guided—as desired —in the direction of thesurface of the contents but instead is broadcast toward the side willlead to transverse resonances (or in the case of a connection stub, tovoid resonances). Moreover, because of the surface waves along theconductive element, longitudinal resonances can develop. The interferingecho signals that this causes can become so strong that the actualuseful echo signal is no longer detectable. Moreover, if longitudinalresonances occur from reflection in the propagation direction, theattenuation of the amplitude of the surface wave and hence of the usefulecho signal is especially problematic.

[0007] One problem that occurs in particular—but not exclusively—whenthe sensor is secured in the connection stub of a container is thedevelopment of deposits. These occur especially in containers that arefilled with hot media or in containers located outdoors that are exposedto major temperature fluctuations. When dust additionally develops inthe container, a deposit then forms that can grow over time to such anextent that the transmission of the surface waves is entirelysuppressed, or that at least interfering echo signals at close range arecreated.

[0008] The object of the invention is to propose a device which iscapable of largely eliminating the influence that a structural partand/or the formation of deposits on the sensor has on the measuringaccuracy and measuring sensitivity of the sensor.

[0009] In a first embodiment of the device of the invention, this objectis attained in that the input unit has at least a length thatcorresponds essentially to the spacing from the container wall to thelower edge of the structural part and is positioned such that thetransition region “input unit conductive element” is locatedapproximately in the plane of the lower edge of the structural part; andthat the diameter of the opening of the input unit at the transitionregion “input unit—conductive element” is on the order of magnitude ofthe wavelength of the high-frequency measurement signals. Because theinput unit is lengthened according to the invention, the structuralparts are located outside the region into which electromagnetic energyis broadcast. The generation of void resonances and interference signalsis therefore largely prevented. A further essential characteristic ofthe invention is that the opening or aperture of the input unit is onthe same order of magnitude as the wavelength of the measurementsignals. This assures that the input unit has a pronounced directionalcharacteristic, and the measurement signals are for the most part inputto the conductive element and thus are not extended back in the oppositedirection along the input unit or broadcast laterally.

[0010] In an alternative embodiment of the device of the invention, theobject is attained in that the input unit has a predetermined length,and is positioned in the container such that the opening of the inputunit, pointing in the direction of the medium, has a certain spacingfrom the corresponding container wall; and that the diameter of theopening of the input unit at the “input unit—conductive element”transition is on the order of magnitude of the wavelength of thehigh-frequency measurement signals. This arrangement is especiallyadvantageous if, although no structural parts that could adverselyaffect the propagation of the measurement signals are located in thevicinity of the input unit, nevertheless there is still an increasedrisk that from condensate formation and dust production in the containerinterior, deposits could form on the input unit. The length and inputshifts the transition region between the input unit and the conductiveelement to a point located farther in the interior of the container,which experience teaches is less vulnerable to the development ofdeposits.

[0011] An advantageous version of the two embodiments of the inventionrecited above provides that the input unit has an inner conductor and anouter conductor; and that between the inner conductor and the outerconductor, in at least a partial region, a dielectric material isdisposed. Since the field symmetry in the coaxial cable is quite similarto the field symmetry in a Sommerfeld or Goubau conductor, at thetransition region “input unit—conductive element” only slight fieldinterference occurs, which is expressed in a high transmission rate andthus high measuring sensitivity. Because of the low proportion ofreflected measurement signals, the interference at close range is alsolow, since multiple reflections between locally lengthy interferencepoints are avoided. The interference points are on the one hand the plugon the electronics, for instance, and on the other the transition region“input unit—conductive element”. Other advantages of this version areconsidered to be that the dielectric material seals off the level sensorfrom the container, and also serves to mechanically retain the innerconductor. If condensate formation in the voids of the input need not befeared, then it is possible, for reasons of cost, to dispense withcompletely filling the three-dimensional region between the innerconductor and the outer conductor with dielectric material.

[0012] It has moreover proved especially advantageous if the dielectricmaterial of the input unit is essentially tapered from the transitionregion “input unit—conductive element” onward, and an upper portion ofthe conductive element is disposed approximately in the region of thelongitudinal axis of the taper. The tapered form of the dielectricmaterial at the same time has several advantages:

[0013] 1. Because of the tapered form, the phase front at the transitionregion “input unit—conductive element” is changed in such a way that animproved directional effect is obtained. Thus on the one hand theundesired broadcasting to the side and to the back is reduced, while onthe other hand the input to the waveguide is improved. Because of thefirst above advantage, the incidence of interfering echoes and so-calledconnection stub ringing is reduced, while because of the secondadvantage above, an increase in the amplitude of the useful echo signalis attained.

[0014] 2. Because of the tapered shape, it is attained that signalcomponents reflected from different points of the taper interfere withone another destructively, which leads to a reduction in the blockdistance. The term “block distance” is understood to be the minimummeasurable distance of a level sensor.

[0015] 3. Because of the tapered shape, the outflow of condensatedroplets is facilitated; this lessens the risk of the formation ofdeposits.

[0016] In a preferred version of the two variants named above forattaining the object of the invention, it is proposed that the outerconductor of the input unit changes over, essentially from thetransition region “input unit conductive element” onward into ahorn-shaped element, and an upper portion of the conductive element isdisposed approximately in the region of the longitudinal axis of thetaper. The advantages of this version are as follows:

[0017] 1. Because of the enlarged aperture of the horn, the directionalaction is improved considerably.

[0018] 2. The horn reduces field distortion in the transition region“input unit—conductive element”, since the outer conductor does not dropaway abruptly but instead widens continuously in diameter. Ideally, thediameter is so large that the surface wave mode already detaches fromthe outer conductor. As a result, there is little field interference atthe transition region “input unit—conductive element”.

[0019] 3. Condensate can flow off on the outside of the horn, so thatthe cross section within which the signal is guided is not closed bydeposits.

[0020] In a third embodiment of the device of the invention, the objectis attained in that the transition region “input unit—conductiveelement” is located essentially in the plane of the container wall; theinput unit has an inner conductor and an outer conductor; that betweenthe inner conductor and the outer conductor, in at least a partialregion, a dielectric material is disposed; and the dielectric materialof the input unit is essentially tapered from the transition region“input unit—conductive element” onward, and an upper portion of theconductive element is disposed approximately in the region of thelongitudinal axis of the taper. In this embodiment as well, the diameterof the aperture of the input unit is preferably on the order ofmagnitude of the wavelength of the measurement signals.

[0021] In a variant of the device of the invention, the object isattained in that the transition region “input unit conductive element”is located essentially in the plane of the container wall; the inputunit has an inner conductor and an outer conductor; that between theinner conductor and the outer conductor, in at least a partial region, adielectric material is disposed; and the outer conductor of the inputunit changes over, essentially from the transition region “inputunit—conductive element” onward into a horn-shaped element, and an upperportion of the conductive element is disposed approximately in theregion of the longitudinal axis of the taper. Once again, preferably thediameter of the aperture of the input unit is on the order of magnitudeof the wavelength of the measurement signals.

[0022] The advantages of these last two versions, with a taper or ahorn-shaped element, have already been explained above. Both versionsare preferably used whenever there are no interfering structural partspositioned in the vicinity of the device of the invention, yet it isimportant not to dispense with the advantages of the invention,particularly with a view to improved directional action, optimizedtransmission, and reduced deposit formation. Because the measurementsignals are input to the conductive element by means of the horn-shapedelement and/or by means of a taper, however, an adequately gooddirectional action is attained even if “interference points” can befound in the immediate vicinity of the transition region “inputunit—conductive element”. It is naturally not unimportant here that ataper and/or a small horn-shaped element is less expensive than a“artificially” lengthened input unit.

[0023] A preferred version of the two variants named above of the deviceof the invention therefore provides that the transition region “inputunit—conductive element” is positioned essentially in the plane of thetop side of a structural part, in particular a connection stub, providedon the container.

[0024] In the fifth embodiment of the device of the invention, theobject is attained in that in the region of the side walls of thestructural part and in the region of the underside of the structuralpart, a conductive material is disposed; and that the transition region“input unit conductive element” is positioned approximately in the planein which the lower edge of the structural part is located. If thestructural part is for instance a connection stub, then it is attainedby this version that no electromagnetic energy can get into theconnection stub. Consequently, no void resonances are generated, either,which has a favorable effect on the block distance. Moreover, thisversion reduces the risk of deposit formation in the critical region ofthe TDR sensor to a minimum.

[0025] An advantageous refinement of the device of the invention recitedabove proposes that a cup-shaped insert part is insertable into theconnection stub, and the insert part is coated on at least one side witha conductive material, or the insert part is made from a conductivematerial.

[0026] In an advantageous refinement of the device of the invention, anopening for receiving the level sensor is provided on the underside ofthe insert part. This makes it possible to use the same measuringinstrument for different installation situations. Only the cup has to beadapted to the dimensions of the connection stub.

[0027] Moreover, one version of the device of the invention provides acover part, which closes off the top side of the connection stub and ofthe insert part. This protects the electronics of the measuringinstrument, since no dirt or water, for instance, can collect in thetop. Moreover, even with narrow connection stubs, it is possible tomount the level sensor in such a way that the indicator and/or controlelements of the sensor remain accessible.

[0028] In a sixth embodiment of the device of the invention, the objectis attained in that the input unit has a length which is essentiallyequivalent to the spacing from the container wall to the lower edge ofthe structural part; that the input unit is positioned such that thetransition region “input unit—conductive element” is locatedapproximately in the plane of the lower edge of the structural part; andthat disposed on the underside of the connection stub in the transitionregion “input unit—conductive element” is a platelike element, which atleast on the side toward the medium in the container is electricallyconductive. This variant of the invention is considered especiallyeconomical.

[0029] An advantageous refinement of the device of the invention, incombination with the variant described above, provides electricalconnecting elements, which are disposed in the region of the outer edgesof the platelike element and in the region of the connection stub. Thepreferably resilient contact elements assure a high-frequency-tightclosure between the plate and the connection stub. Consequently, therisk that some of the energy of the transmitted signals will bereflected back into the connection stub and there induce the highlyunwanted void resonances, is quite low.

[0030] In a seventh embodiment of the device of the invention, theobject is attained in that the transition region “input unit—conductiveelement” is disposed in the plane in which the top side of thestructural part is located; that the conductive element is modified,approximately over the length of the structural part or over the lengththat is equivalent to the distance between the corresponding containerwall and the lower edge of the structural part, in such a way that inthis region virtually no interactions occur between the measurementsignals, carried along the conductive element, and the structural part.

[0031] An advantageous refinement of the device of the inventionprovides that the conductive element, over the length that is equivalentto the distance between the corresponding container wall and the loweredge of the structural part, is made from a material of low electricalconductivity and/or high magnetic permeability.

[0032] It is also provided that the surface of the conductive element,over the length of the structural part or over the length that isequivalent to the distance between the corresponding container wall andthe lower edge of the structural part, has a roughened surfacestructure. Alternatively or in addition, it is provided the surface ofthe conductive element, over the length of the structural part or overthe length that is equivalent to the distance between the correspondingcontainer wall and the lower edge of the structural part, has a surfacestructure by which the longitudinal inductance of the conductive elementis increased. As an example, a helical surface structure can be named.

[0033] One advantageous version of the device of the invention isconsidered to be that the conductive element, over the length of thestructural part or over the length that is equivalent to the distancebetween the corresponding container wall and the lower edge of thestructural part, has an insulating layer, whose magnetic and/ordielectrical properties are dimensioned such that the length of theelectromagnetic fields is limited to the region at close range to theconductive element.

[0034] The aforementioned versions are distinguished by the fact thatthe field length is reduced in a targeted way in those regions wherethere is a risk of an unwanted interaction with built-in fittings, butnot over the remaining length of the conductive element. Here,especially if deposits form on the conductive element, a short fieldlength would lead to severe damping of the measurement signals.

[0035] In an eighth embodiment of the device of the invention, theobject is attained in that the transition region “input unit—conductiveelement” is disposed in the plane of the container wall; that theconductive element, at least in the upper region, is made from amaterial of low electrical conductivity and/or high magneticpermeability; and/or that the conductive element at least in the upperregion has a roughened surface structure; and/or that the conductiveelement at least in the upper region has a surface structure by whichthe longitudinal inductance of the conductive element is increased;and/or that the conductive element at least in the upper region has aninsulating layer, whose magnetic and/or dielectric properties aredimensioned such that the length of the electromagnetic fields islimited to the region at close range to the conductive element.

[0036] These variants of the embodiment of the invention haveessentially two decisive advantages:

[0037] The directional action is improved, since because of the lesserfield length, the aperture is effectively increased and the directionalcharacteristic is improved. Thus there are fewer problems fromelectromagnetic fields broadcast laterally into the container, whichafter multiple reflections in the container could cause an interferingbackground. Moreover, because of the lesser field length of themeasurement signals traveling along the conductive element, the abruptchange in wave resistance at the transition from the input unit to theconductive element is ameliorated. This is expressed in a highertransmission rate, and thus a lower reflection rate, of the measurementsignals.

[0038] The invention will be described in further detail in conjunctionwith the following drawings. Shown are:

[0039]FIG. 1: a schematic illustration of a first embodiment of thedevice of the invention;

[0040]FIG. 2: a schematic illustration of a second embodiment of thedevice of the invention;

[0041]FIG. 3: a schematic illustration of a third embodiment of thedevice of the invention;

[0042]FIG. 4: a schematic illustration of a fourth embodiment of thedevice of the invention;

[0043]FIG. 5: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 3;

[0044]FIG. 6: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 4;

[0045]FIG. 7: a schematic illustration of a fifth embodiment of thedevice of the invention;

[0046]FIG. 8: a schematic illustration of an advantageous version of theembodiment of the device of the invention shown in FIG. 7;

[0047]FIG. 9: a schematic illustration of a sixth embodiment of thedevice of the invention;

[0048]FIG. 10: a schematic illustration of a seventh embodiment of thedevice of the invention;

[0049]FIG. 11: a schematic illustration of an eighth embodiment of thedevice of the invention; and

[0050]FIG. 12: a schematic illustration of a preferred version of theconductive element.

[0051]FIG. 1 is a schematic illustration of a first embodiment of thelevel sensor 1 of the invention. The level sensor comprises atransceiver 29, a coaxial cable, an input unit 2, and a conductiveelement 7. The evaluation of the echo signals is done in an evaluationunit, not shown separately in FIG. 1.

[0052] In the case shown, the input unit 2 has a length that is greaterthan the length of the connection stub 4. The input unit 2 is disposedsuch that the opening 8 is in the vicinity of—in this case, below—thelower edge 5 of the connection stub 4. It is understood that the opening8 can also be placed above the lower edge 5. Moreover, the opening 8 inthe input unit 2 is dimensioned such that it is on the order ofmagnitude of the wavelength of the measurement signals guided by thelevel sensor 1. To a very great extent, the embodiment according to theinvention prevents components of the measurement signals from enteringthe connection stub 4. Consequently, virtually no void resonances areexcited, which is expressed in a considerable improvement in themeasuring accuracy of the level sensor 1. In the case shown, thethree-dimensional region between the inner conductor 9 and the outerconductor 10 is furthermore filled with a dielectric material 11. Theadvantages of this embodiment have already been explained at lengthabove and will not be repeated here. To increase the directional actionof the level sensor 1, the dielectric material 11 is tapered, from thetransition region 6 between the input unit 2 and the conductive element7 onward. It is understood that the taper 12 can have the most variousembodiments. In FIG. 2, a schematic illustration of a second embodimentof the device of the invention is shown, which essentially differs fromthe version shown in FIG. 1 only in that it is disposed not in aconnection stub 4 but rather directly on the contained wall 3. Theadvantages of this embodiment of the invention have also already beenaddressed in detail above.

[0053] A schematic illustration of a third embodiment of the device ofthe invention can be seen in FIG. 3. Here, the transition region 6between the input unit 2 and the conductive element 7 is disposed suchthat it is located virtually in the plane of the container wall 3. Theinput unit 2 has an inner conductor 9 and an outer conductor 10. Betweenthe two parts, a dielectric material 11 is disposed. The dielectricmaterial 11 of the input unit 2 is tapered, approximately from thetransition region 6 “input unit 2—conductive element 7” onward, and anupper portion of the conductive element 7 is disposed approximately inthe region of the longitudinal axis of the taper 12. As the primaryadvantages of this embodiment, the excellent directional action, theshort block distance, and the reduced risk of deposit formation can benamed. To improve the directional action still further, the outerconductor 13 is widened, from the transition region 6 “input unit2—conductive element 7” onward, into a horn-shaped element 13.

[0054] In FIG. 4, a schematic illustration of a fourth embodiment of thedevice of the invention is shown. Once again, the transition region 6“input unit 2—conductive element 7” is disposed such that it is locatedvirtually in the plane of the container wall 3. The input unit 2comprises an inner conductor 9 and an outer conductor 10, and adielectric material 13 can be found between the inner conductor 9 andthe outer conductor 10. As already noted above, it is unnecessary forthe dielectric material 11 to fill the entire three-dimensional regionbetween the inner conductor 9 and the outer conductor 10. The outerconductor 10 of the input unit 2 is widened, approximately from thetransition region 6 “input unit 2—conductive element 7” onward, in sucha way that it forms a horn-shaped element 13. An upper portion of theconductive element 7 is disposed approximately in the region of thelongitudinal axis of the horn-shaped element 13. Since the advantages ofthis embodiment have already been described at length above, it sufficesat this point to list them briefly: improved directional action, reducedfield distortion at the transition region 6 “input unit 2—conductiveelement 7”, and thus an increased transmission rate and greatly reducedrisk of deposit formation.

[0055] The embodiments shown in FIGS. 5 and 6 correspond to those ofFIGS. 3 and 4, except that here the level sensors 1 are disposed in theconnection stub 4 of a container 3.

[0056] It is quite favorable if the input unit 2 is placed in a greatlyextended metal plate. The metal plate improves the electrical adaptationof the conductive element 7 and prevents the broadcasting ofelectromagnetic energy to the rear. The metal plate acts on the order ofan electrical mirror.

[0057]FIG. 7 is a schematic illustration of a fifth embodiment of thedevice of the invention. A connection stub 4 is provided in thecontainer wall 3. A conductive material 20 is disposed on the side walls17, 18 and in the region of the underside 19 of the connection stub 4.Preferably, this is a cup-shaped insert element 21, which is adapted tothe dimensions of the connection stub 4.

[0058] The level sensor 1, comprising the transceiver 29, input unit 2,and conductive element 7, is embodied in this case shown as a compactsensor and is positioned in an opening 22 on the underside 19 of thecup-shaped insert element 21. The input unit 2 is positioned in theconnection stub 4 in such a way that the transition region 6 “input unit2—conductive element 7” comes to be located essentially in the plane ofthe container wall 3. It is understood that for the sake of exhaustingthe aforementioned advantages, it is also possible to provide a taper 12and/or a horn-shaped element 13 in addition at the transition region 6“input unit 2—conductive element 7”.

[0059]FIG. 8 shows a schematic illustration of an advantageous versionof the embodiment of the device of the invention shown in FIG. 7. Itdiffers from the variant shown in FIG. 7 essentially only in the coverpart 23, which closes off the cup-shaped insert part 21, disposed in theconnection stub 4, from the outside. This version will always be usedwhenever the TDR sensor i on the one hand is to be protected againstenvironmental factors, yet its control and display elements need toremain readily accessible.

[0060] In FIG. 9, a schematic illustration of a sixth embodiment of thedevice of the invention can be seen, which is distinguished by lowproduction costs. The input unit 2 has a length which is essentiallyequivalent to the length of the connection stub 4. The input unit 2 ispositioned such that the transition region 6 “input unit 2—conductiveelement 7” is located approximately in the plane of the lower edge 5 ofthe connection stub 4. In the transition region 6 “input unit2—conductive element 7”, on the underside 19 of the connection stub 4, aplatelike element 24 is disposed, which is electrically conductive atleast on the side oriented toward the contents in the container. In theregion of the outer edges 26 of the platelike element 24, connectingelements 25 of an electrically conductive material are provided. Theseconnecting or contact elements 25 are preferably embodied resiliently.They assure a high-frequency-tight closure between the platelike element24 and the connection stub 4, whose side walls 17, 18 are either madefrom an electrically conductive material or at least lined with anelectrically conductive material. As a result, as already noted severaltimes, the risk that some of the energy of the transmission signals willget back into the connection stub is reduced.

[0061]FIG. 10 shows a schematic illustration of a seventh embodiment ofthe device of the invention. The transition region 6 “input unit2—conductive element 7” is disposed in the plane in which the top side16 of the connection stub 4 is located. The conductive element 7 ismodified, approximately over the length of the connection stub 4 (or ingeneral terms, over the length that is equivalent to the distancebetween the corresponding container wall 3 and the lower edge 5 of therespective structural part or built-in part), in such a way that in thisregion, virtually no interactions occur between the measurement signals,guided along the conductive element 7, and the connection stub 4 (or ingeneral the structural part). The version shown in FIG. 11 differs fromthe version shown in FIG. 10 only in that it is not secured in theregion of a connection stub 4.

[0062] There are many possibilities by way of which—each taken byitself, or in combination with at least one other variant—theaforementioned goal can be attained:

[0063] The conductive element 7, at least in its upper region, is madefrom a material of low electrical conductivity and/or high magneticpermeability;

[0064] the conductive element 7, at least in the upper region, has aroughened surface structure;

[0065] the conductive element 7, at least in the upper region, has asurface structure by which the longitudinal inductance of the conductiveelement is increased;

[0066] the conductive element 7, as explicitly shown in FIG. 10 and FIG.11, at least in the upper region, has an insulating layer 28, whosemagnetic and/or dielectric properties are dimensioned such that thelength of the electromagnetic fields is limited to the region at closerange to the conductive element 7.

[0067] In FIG. 12, a schematic illustration of a preferred embodiment ofthe conductive element 7 can be seen. The conductive element 7 is madefrom a high-permeability material, the effect of which is only a slightfield length of the service wave guided along the conductive element 7.In addition, the surface of the conductive element 7 is not smooth butinstead has a roughened structure, which likewise contributes to aconsiderable field reduction. If for instance the surface of theconductive element 7 is made helical, then an increase in thelongitudinal inductance is achieved. The wave resistance is increased,and the field length is reduced.

[0068] Moreover, at least in the region adjoining the input unit, theconductive element has an insulating layer 29, which has magnetic anddielectric properties adapted such that simultaneously the field lengthof the measurement signals guided along the conductive element 7 arereduced down to the desired amount. A further advantage of asufficiently thick insulating layer 29 is moreover that the measuringaccuracy of the level sensor 1 is virtually independent of any depositformation.

List of Reference Numerals

[0069]1 Level sensor

[0070]2 Input unit

[0071]3 Container wall

[0072]4 Structural part, such as connection stub

[0073]5 Lower edge of the structural part

[0074]6 Transition region

[0075]7 Conductive element

[0076]8 Opening of the input unit

[0077]9 Inner conductor

[0078]10 Outer conductor

[0079]11 Dielectric material

[0080]12 Taper

[0081]13 Horn-shaped element

[0082]14 Longitudinal axis

[0083]15 Upper portion of the conductive element

[0084]16 Upper portion of the connection stub

[0085]17 Side wall of the connection stub

[0086]18 Side wall of the connection stub

[0087]19 Underside of the connection stub

[0088]20 Conductive material

[0089]21 Insert part/cup-shaped element

[0090]22 Opening

[0091]23 Cover part

[0092]24 Platelike element

[0093]25 Connecting element

[0094]26 Outer edge

[0095]27 Surface of the conductive element

[0096]28 Insulating layer

[0097]29 Transceiver

1. A device for determining and/or monitoring the level of contents, orthe location of the boundary face between two media or phases, in acontainer, in which on the container at least one structural part isprovided, on which or in whose surroundings at least thesensor-associated part of the device is mounted, having a signalgenerating unit, which generates high-frequency measurement signals,having an input unit and a conductive element, the measurement signalsbeing input to the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, characterized in thatthe input unit (2) has at least a length that corresponds essentially tothe spacing from the container wall (3) to the lower edge (5) of thestructural part (4) and is positioned such that the transition region“input unit conductive element” (6) is located approximately in theplane of the lower edge (5) of the structural part (4); and that thediameter of the opening (8) of the input unit (2) at the transitionregion “input unit—conductive element” (6) is on the order of magnitudeof the wavelength of the high-frequency measurement signals.
 2. A devicefor determining and/or monitoring the level of contents, or the locationof the boundary face between two media or phases, in a container, havinga signal generating unit, which generates high-frequency measurementsignals, having an input unit and a conductive element, the measurementsignals being input to the conductive element via the input unit, andhaving a receiving/evaluating unit, which directly or indirectly via thetransit time of the measurement signals, reflected from the surface orboundary face of the contents, determines the level of the contents orthe location of the boundary face in the container, characterized inthat the input unit (2) has a predetermined length, and is positioned inthe container such that the opening (8) of the input unit (2), pointingin the direction of the medium, has a certain spacing from thecorresponding container wall (3); and that the diameter of the opening(8) of the input unit (2) at the “input unit—conductive element”transition (6) is on the order of magnitude of the wavelength of thehigh-frequency measurement signals.
 3. The device of claim 1 or 2,characterized in that the input unit (2) has an inner conductor (9) andan outer conductor (10); and that between the inner conductor (9) andthe outer conductor (19), in at least a partial region, a dielectricmaterial is disposed.
 4. The device of claim 1, 2 or 3, characterized inthat the dielectric material (11) of the input unit (2) is essentiallytapered from the transition region “input unit conductive element” (6)onward, and an upper portion of the conductive element (7) is disposedapproximately in the region of the longitudinal axis (14) of the taper(12).
 5. The device of claim 1, 2, 3 or 4, characterized in that theouter conductor (10) of the input unit (2) changes over, essentiallyfrom the transition region “input unit conductive element” (6) onwardinto a horn-shaped element (13), and an upper portion of the conductiveelement (7) is disposed approximately in the region of the longitudinalaxis (14) of the taper (12).
 6. A device for determining and/ormonitoring the level of contents, or the location of the boundary facebetween two media or phases, in a container, having a signal generatingunit, which generates high-frequency measurement signals, having aninput unit and a conductive element, the measurement signals being inputto the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, characterized in thatthe transition region “input unit—conductive element” (6) is locatedessentially in the plane of the container wall (3); the input unit (2)has an inner conductor (9) and an outer conductor (10); that between theinner conductor (9) and the outer conductor (10), in at least a partialregion, a dielectric material is disposed; and the dielectric material(11) of the input unit (2) is essentially tapered from the transitionregion “input unit conductive element” (6) onward, and an upper portionof the conductive element (7) is disposed approximately in the region ofthe longitudinal axis (14) of the taper (12).
 7. A device fordetermining and/or monitoring the level of contents, or the location ofthe boundary face between two media or phases, in a container, having asignal generating unit, which generates high-frequency measurementsignals, having an input unit and a conductive element, the measurementsignals being input to the conductive element via the input unit, andhaving a receiving/evaluating unit, which directly or indirectly via thetransit time of the measurement signals, reflected from the surface orboundary face of the contents, determines the level of the contents orthe location of the boundary face in the container, characterized inthat the transition region “input unit—conductive element” (6) islocated essentially in the plane of the container wall (3); the inputunit (2) has an inner conductor (9) and an outer conductor (10); thatbetween the inner conductor (9) and the outer conductor (10), in atleast a partial region, a dielectric material is disposed; and the outerconductor (10) of the input unit (2) changes over, essentially from thetransition region “input unit conductive element” (6) onward into ahorn-shaped element (13), and an upper portion of the conductive element(7) is disposed approximately in the region of the longitudinal axis(14) of the taper (12).
 8. The device of claim 6 or 7, characterized inthat the transition region “input unit—conductive element” (6) ispositioned essentially in the plane of the top side (16) of a structuralpart (4), in particular a connection stub, provided on the container. 9.A device for determining and/or monitoring the level of contents, or thelocation of the boundary face between two media or phases, in acontainer, in which on the container at least one structural part, inparticular a connection stub, is provided, in which at least thesensor-associated part of the device is mounted, having a signalgenerating unit, which generates high-frequency measurement signals,having an input unit and a conductive element, the measurement signalsbeing input to the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, characterized in that inthe region of the side walls (17, 18) of the structural part (4) and inthe region of the underside (19) of the structural part (4), aconductive material (20) is disposed; and that the transition region“input unit—conductive element” (6) is positioned approximately in theplane in which the lower edge (5) of the structural part (4) is located.10. The device of claim 9, characterized in that a cup-shaped insertpart (21) is insertable into the connection stub (4), and the insertpart (21) is coated on at least one side with a conductive material, orthe insert part (21) is made from a conductive material.
 11. The deviceof claim 9 or 10, characterized in that an opening (22) for receivingthe level sensor (1) is provided on the underside (19) of the insertpart (21).
 12. The device of claim 9, 10 or 11, characterized in that acover part (23) is provided, which closes off the top side (16) of theconnection stub (4) and of the insert part (21).
 13. A device fordetermining and/or monitoring the level of contents, or the location ofthe boundary face between two media or phases, in a container, in whichon the container at least one structural part, in particular aconnection stub, is provided, in or on the connection stub at least thesensor-associated part of the device is mounted, having a signalgenerating unit, which generates high-frequency measurement signals,having an input unit and a conductive element, the measurement signalsbeing input to the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, characterized in thatthe input unit (2) has a length which is essentially equivalent to thespacing from the container wall (3) to the lower edge (5) of thestructural part (4); that the input unit (2) is positioned such that thetransition region “input unit—conductive element” (6) is locatedapproximately in the plane of the lower edge (5) of the structural part(4); and that disposed on the underside (19) of the connection stub (4)in the transition region “input unit—conductive element” (6) is aplatelike element (24), which at least on the side toward the medium inthe container is electrically conductive.
 14. The device of claim 13,characterized in that electrical connecting elements (25) are provided,which are disposed in the region of the outer edges (26) of theplatelike element (25) and in the region of the connection stub (4). 15.A device for determining and/or monitoring the level of contents, or thelocation of the boundary face between two media or phases, in acontainer, in which on the container at least one structural part, inparticular a connection stub, is provided, in or on the connection stubat least the sensor-associated part of the device is mounted, having asignal generating unit, which generates high-frequency measurementsignals, having an input unit and a conductive element, the measurementsignals being input to the conductive element via the input unit, andhaving a receiving/evaluating unit, which directly or indirectly via thetransit time of the measurement signals, reflected from the surface orboundary face of the contents, determines the level of the contents orthe location of the boundary face in the container, characterized inthat the transition region “input unit—conductive element” (6) isdisposed in the plane in which the top side (16) of the structural part(4) is located; that the conductive element (7) is modified,approximately over the length of the structural part (4) or over thelength that is equivalent to the distance between the correspondingcontainer wall (3) and the lower edge (5) of the structural part (4), insuch a way that in this region virtually no interactions occur betweenthe measurement signals, carried along the conductive element (7), andthe structural part (4).
 16. The device of claim 15, characterized inthat at least the surface of the conductive element (7) to at least theskin depth, at the measurement frequencies employed, over the length ofthe structural part (4) or over the length that is equivalent to thedistance between the corresponding container wall (3) and the lower edgeof the structural part (4), is made from a material of low electricalconductivity and/or high magnetic permeability.
 17. The device of claim15 or 16, characterized in that the surface (27) of the conductiveelement (7), over the length of the structural part or over the lengththat is equivalent to the distance between the corresponding containerwall (3) and the lower edge (5) of the structural part (4), has aroughened surface structure.
 18. The device of claim 15, 16 or 17,characterized in that the surface (27) of the conductive element (7),over the length of the structural part or over the length that isequivalent to the distance between the corresponding container wall (3)and the lower edge (5) of the structural part (4), has a surfacestructure, by which the longitudinal inductance of the conductiveelement (7) is increased.
 19. The device of claim 15, 16, 17 or 18,characterized in that the conductive element (7), over the length of thestructural part or over the length that is equivalent to the distancebetween the corresponding container wall (3) and the lower edge (5) ofthe structural part (4), has an insulating layer (28), whose magneticand/or dielectrical properties are dimensioned such that the length ofthe electromagnetic fields is limited to the region at close range tothe conductive element (7).
 20. A device for determining and/ormonitoring the level of contents, or the location of the boundary facebetween two media or phases, in a container, having a signal generatingunit, which generates high-frequency measurement signals, having aninput unit and a conductive element, the measurement signals being inputto the conductive element via the input unit, and having areceiving/evaluating unit, which directly or indirectly via the transittime of the measurement signals, reflected from the surface or boundaryface of the contents, determines the level of the contents or thelocation of the boundary face in the container, characterized in thatthe transition region “input unit—conductive element” (6) is disposed inthe plane of the container wall (3); that the conductive element (7), atleast in the upper region, is made from a material of low electricalconductivity and/or high magnetic permeability; and/or that theconductive element (7) at least in the upper region has a roughenedsurface structure; and/or that the conductive element (7) at least inthe upper region has a surface structure by which the longitudinalinductance of the conductive element is increased; and/or that theconductive element (7) at least in the upper region has an insulatinglayer (28), whose magnetic and/or dielectric properties are dimensionedsuch that the length of the electromagnetic fields is limited to theregion at close range to the conductive element (7).